Polyester Polymer Compositions

ABSTRACT

A fiber reinforced polyester polymer composition is disclosed that contains at least one tribological modifier. The tribological modifier may comprise an ultra-high molecular weight silicone alone or in combination with polyytetrafluoroethylene particles. The composition not only has excellent tensile properties but also can produce a low friction surface.

RELATED APPLICATIONS

The present application is based upon and claims priority to U.S. patentapplication Ser. No. 15/915,350, filed on Mar. 8, 2018, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/469,874,filed on Mar. 10, 2017, which are both incorporated herein by referencein their entirety.

BACKGROUND

Engineering thermoplastics and elastomeric materials are often used innumerous and diverse applications in order to produce molded parts andproducts. For instance, polyester polymers and polyester elastomers areused to produce all different types of molded products, such asinjection molded products, blow molded products, and the like. Polyesterpolymers, for instance, can be formulated in order to be chemicallyresistant, to have excellent strength properties and, when formulatingcompositions containing polyester elastomers, to be flexible. Ofparticular advantage, polyester polymers can be melt processed due totheir thermoplastic nature. In addition, polyester polymers can berecycled and reprocessed.

In certain applications, thermoplastic polymers, such as polyesterpolymers, are combined with fibrous fillers in order to increase themodulus and/or tensile strength of parts and products made from thereinforced composition. Problems have been experienced in the past,however, in incorporating reinforcing fibers into a polyester polymermatrix that has the desired balance of properties. For instance,polyester polymer composites containing reinforcing fibers may haveadequate strength properties but can experience an increase in surfacefriction when moved across an adjacent surface. The increase infriction, for instance, can cause abrasive wear after extended periodsof use. These problems can become exacerbated when a first part madefrom the polyester polymer matrix is designed to slide or rub against anadjacent part made from the same reinforced polyester matrix.

In view of the above, a need currently exists for reinforced polyesterpolymer compositions that can be formulated so as to have a desiredbalance of physical properties and characteristics. More particularly, aneed exists for a fiber reinforced polyester polymer composition thatalso has reduced friction properties.

SUMMARY

The present disclosure is generally directed to a polyester polymercomposition containing reinforcing fibers for increasing tensilestrength in combination with a tribological additive package that hasbeen found to dramatically decrease the coefficient of frictioncharacteristics of articles molded from the composition. Parts andarticles can be made in accordance with the present disclosure that notonly have excellent strength characteristics and properties but thatalso are well suited for use in applications where the parts or articlesare intended to slide against an opposing surface. For instance, thearticles and products can be formulated so as to produce no audiblenoise when sliding against an opposing component or part, especiallywhen the opposing component or part is also made from the same or asimilar polymer composition.

In one embodiment, for instance, the polymer composition of the presentdisclosure comprises a polyester polymer comprising a polybutyleneterephthalate polymer. The polybutylene terephthalate polymer can bepresent alone or in combination with other polymers within thecomposition. The other polymers may comprise, for instance, a differentpolyester polymer such as polyethylene terephthalate, a polycarbonatepolymer, and the like. The polymer composition also contains reinforcingfibers, such as glass fibers. The reinforcing fibers can be present inthe composition generally in an amount greater than about 5% by weight,such as in an amount greater than about 10% by weight, such as in anamount greater than about 15% by weight. The reinforcing fibers aregenerally present in an amount less than about 55% by weight, such as inan amount less than about 45% by weight, such as in an amount less thanabout 35% by weight.

In accordance with the present disclosure, the polymer compositionfurther contains at least one tribological modifier. The tribologicalmodifier, in one embodiment, can comprise an ultra-high molecular weightsilicone. The ultra-high molecular weight silicone can have a kinematicviscosity of greater than about 100,000 mm² s⁻¹. For example, theultra-high molecular weight silicone can be present in the polymercomposition in an amount from about 0.1% to about 10% by weight, such asfrom about 0.5% to about 3% by weight. In one embodiment, the ultra-highmolecular weight silicone comprises a polydimethylsiloxane.

In an alternative embodiment, the tribological modifier contained withinthe polymer composition may comprise a polytetrafluoroethylene polymer.The polytetrafluoroethylene polymer may be present alone or incombination with an ultra-high molecular weight silicone.

In one particular embodiment, the polymer composition comprises apolybutylene terephthalate polymer in an amount from about 50% to about90% by weight, reinforcing fibers such as glass fibers being present inthe composition in an amount from about 5% to about 30% by weight, anultra-high molecular weight silicone being present in the composition inan amount from about 0.5% to about 4% by weight and apolytetrafluoroethylene polymer being present in the composition in anamount from about 1% to about 20% by weight.

As described above, the polymer composition can be formulated to havelow friction properties. For instance, the polymer composition canexhibit a dynamic coefficient of friction according to VDA 230-206 ofless than about 0.08 when tested against polycarbonate containing 15% byweight polytetrafluoroethylene and 20% by weight glass fiber or whentested against polybutylene terephthalate containing 15% by weightpolytetrafluoroethylene and 20% by weight glass fiber, or when testedagainst itself at a speed of 8 mm/s, at a load of 30 N and after 1,000cycles. In one embodiment, the polymer composition may exhibit a dynamiccoefficient of friction of less than about 0.07, such as less than about0.05 when tested against the above materials.

When an ultra-high molecular weight silicone is present in thecomposition, the silicone can be added with a carrier. In oneembodiment, for instance, the ultra-high molecular weight silicone canbe grafted to silica and added to the composition. Alternatively, theultra-high molecular weight silicone may be combined with a carrierpolymer prior to being blended with the other components. The carrierpolymer, for instance, may comprise a polycarbonate polymer or apolyester polymer. The polyester polymer, for instance, may comprisepolyethylene terephthalate, a copolyester, and/or a polyester elastomer.

In one embodiment, the polymer composition of the present disclosure isformulated for producing medical products. When producing medicalproducts, for instance, the polymer composition can be formulated to beisocyanate-free.

In one embodiment, the polymer composition can be used to producemedical inhalers, injectors, and the like. The medical product, forinstance, may include a first sliding member in operative associationwith a second sliding member. The first sliding member and the secondsliding member may be positioned to remain in contact and move relativeto each other. At least one of the sliding members can be made from thepolymer composition of the present disclosure. In one embodiment, forinstance, both sliding members are made from the polymer composition ofthe present disclosure.

Other features and aspects of the present disclosure are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present disclosure is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures, in which:

FIG. 1 is a perspective view of a medical inhaler made in accordancewith the present disclosure; and

FIG. 2 is a side view of a medical injector that may be made inaccordance with the present disclosure.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentdisclosure.

In general, the present disclosure is directed to a polyester polymercomposition and to polymer articles made from the composition that notonly have increased strength properties but also have improvedtribological properties such as low friction properties. The polyesterpolymer composition contains reinforcing fibers for increasing thestrength of the composition. The reinforcing fibers, however, canincrease the friction characteristics of the composition and causeabrasive wear when placed in use. In order to counterbalance thepresence of the reinforcing fibers, the polymer composition contains atribological stabilizer package. The tribological additive package cancomprise the presence of at least one tribological modifier, such as anultra-high molecular weight silicone, a polytetrafluoroethylene polymer,or combinations thereof.

The composition of the present disclosure can be formulated for medicalapplications. For example, when used in medical applications, thepolymer composition can contain no isocyanates, epoxy resins,carbodiimides or other similar compounds. In certain applications,medical devices are needed in which the parts are not only made fromhigh strength materials but that can provide ultra-low friction andreduced wear for parts that are intended to slide against an adjacentsurface. As will be described in greater detail below, polymercompositions made according to the present disclosure have not onlyexcellent strength properties but can display extremely low frictionproperties without the need of applying external lubricants.

When two opposing surfaces slide against each other, the surfaces reactin a way that is referred to as the stick-slip phenomenon. Thestick-slip phenomenon refers to the manner in which two opposingsurfaces or articles slide over each other in reaction to the forces offriction. Static friction refers to the friction between two or moreobjects that are not moving relative to each other. Kinetic friction, onthe other hand, occurs when two objects are moving relative to eachother while remaining in contact. In order for one object to sliderelative to another object, enough force must be exerted on one objectto overcome the forces of static friction. When movement between the twoobjects occurs, a reduction of the friction between the two surfaces cancause a sudden increase in the velocity of movement. In other words,once one object moves relative to another object, in some applications,less force is needed to continue movement. The friction between the twosurfaces can increase or decrease during movement depending uponnumerous factors, including the speed at which movement continues.Stick-slip describes how surfaces alternate between sticking to eachother and sliding over each other as movement occurs between twosurfaces and as the conditions of movement change.

Polymer articles that have a relatively high coefficient of friction notonly require greater amounts of force in order to slide one materialover the other but also can be prone to wear. Over time, for instance,the materials can begin to degrade due to the forces of friction.

As two surfaces move relative to each other and the stick-slipphenomenon occurs, noise can also be generated from the two surfaces.Depending upon the stick-slip properties of the materials, noisegeneration can be highly audible or very quiet. In many applications,the generation of noise caused by the stick-slip phenomenon when twocomponents are sliding against each other is highly undesirable. Forinstance, when designing and manufacturing medical devices and consumerproducts, manufacturers and engineers try to design products so that nonoise generation occurs when the products are in use. Noise generationduring use of the product, for instance, can create an impression withthe consumer that the product is of inferior quality and made withinexpensive materials.

The present disclosure is particularly directed to a polymer compositionthat can be used to make molded parts such that when the parts slideagainst each other excessive wear and/or noise generation is inhibitedand even eliminated.

For example, in one embodiment, the present disclosure is directed to alow friction assembly that includes a first sliding member in operativeassociation with a second sliding member. The first sliding member andthe second sliding member can both be made from a polymer compositionformulated in accordance with the present disclosure. When testedagainst each other, the composition can be formulated so as to exhibit adynamic coefficient of friction of less than about 0.08, such as lessthan about 0.07, such as less than about 0.06, such as less than about0.05. The compositions or molded parts can be tested against each otheraccording to a stick-slip test having Test No. VDA 230-206.

Specimens tested using the above method can also be analyzed to measurea wear track width which is an abrasion width. In accordance with thepresent disclosure, the compositions and molded articles can exhibit awear track width of less than 0.3 mm, such as less than about 0.25 mm,such as even less than about 0.2 mm when tested at a force of 30 N andat a velocity of 8 mm/s after 1,000 cycles.

Polyester Polymer

The polymer composition of the present disclosure generally contains apolyester polymer in combination with reinforcing fibers and atribological additive package. The polyester polymer generally comprisesa polyalkylene terephthalate polymer.

Polyalkylene terephthalate polymers suitable for use herein are derivedfrom an aliphatic or cycloaliphatic diol, or mixtures thereof,containing from 2 to about 10 carbon atoms and an aromatic dicarboxylicacid.

The polyesters which are derived from a cycloaliphatic diol and anaromatic dicarboxylic acid are prepared by condensing either the cis- ortrans-isomer (or mixtures thereof) of, for example,1,4-cyclohexanedimethanol with the aromatic dicarboxylic acid.

Examples of aromatic dicarboxylic acids include isophthalic orterephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4′-dicarboxydiphenylether, etc., and mixtures of these. All of these acids contain at leastone aromatic nucleus. Fused rings can also be present such as in 1,4- or1,5- or 2,6-naphthalene-dicarboxylic acids. In one embodiment, thedicarboxylic acid is terephthalic acid or mixtures of terephthalic andisophthalic acid.

In one embodiment, the polyalkylene terephthalate polymer present in thepolymer composition comprises a polybutylene terephthalate polymer. Forexample, the polymer composition may contain a polybutyleneterephthalate polymer in an amount greater than about 30% by weight,such as in an amount greater than about 40% by weight, such as in anamount greater than about 50% by weight, such as in an amount greaterthan about 60% by weight, such as in an amount greater than about 70% byweight. The polybutylene terephthalate polymer is generally present inan amount less than about 90% by weight, such as in an amount less thanabout 80% by weight.

The polymer composition may contain the polybutylene terephthalatepolymer alone or in combination with other thermoplastic polymers. Forinstance, the polybutylene terephthalate polymer may be combined withother polyester polymers and/or a polycarbonate polymer. Other polyesterpolymers that may be present in the composition include a polyethyleneterephthalate polymer or a polyethylene terephthalate copolymer. Forinstance, a polyethylene terephthalate copolymer or modifiedpolyethylene terephthalate polymer can be produced with a modifying acidor a modifying diol.

As used herein, the terms “modifying acid” and “modifying diol” aremeant to define compounds, which can form part of the acid and diolrepeat units of a polyester, respectively, and which can modify apolyester to reduce its crystallinity or render the polyester amorphous.In one embodiment, however, the polyesters present in the polymercomposition of the present disclosure are non-modified and do notcontain a modifying acid or a modifying diol.

Examples of modifying acid components may include, but are not limitedto, isophthalic acid, phthalic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexane dicarboxylic acid, 2,6-naphthaline dicarboxylic acid,succinic acid, glutaric acid, adipic acid, sebacic acid, suberic acid,1,12-dodecanedioic acid, and the like. In practice, it is oftenpreferable to use a functional acid derivative thereof such as thedimethyl, diethyl, or dipropyl ester of the dicarboxylic acid. Theanhydrides or acid halides of these acids also may be employed wherepractical. Preferred is isophthalic acid.

Examples of modifying diol components may include, but are not limitedto, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,2-propanediol,1,3-propanediol, 2-Methy-1,3-propanediol, 1,4-butanediol,1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,2,2,4,4-tetramethyl 1,3-cyclobutane diol,Z,8-bis(hydroxymethyltricyclo-[5.2.1.0]-decane wherein Z represents 3,4, or 5; 1,4-Bis(2-hydroxyethoxy)benzene, 4,4′-Bis(2-hydroxyethoxy)diphenylether [Bis-hydroxyethyl Bisphenol A],4,4′-Bis(2-hydroxyethoxy)diphenylsulfide [Bis-hydroxyethyl Bisphenol S]and diols containing one or more oxygen atoms in the chain, e.g.diethylene glycol, triethylene glycol, dipropylene glycol, tripropyleneglycol, and the like. In general, these diols contain 2 to 18,preferably 2 to 8 carbon atoms. Cycloalphatic diols can be employed intheir cis or trans configuration or as mixtures of both forms.

When present, the polyester polymer or polycarbonate polymer combinedwith the polybutylene terephthalate can be added to the polymercomposition in amounts generally greater than about 5% by weight, suchas in amounts greater than about 10% by weight, such as in amountsgreater than about 15% by weight, such as in amounts greater than about20% by weight. The polyester polymer or polycarbonate polymer isgenerally present in an amount less than about 40% by weight, such as inan amount less than about 30% by weight, such as in an amount less thanabout 20% by weight, such as in an amount less than about 15% by weight.

Reinforcing Fibers

The polymer composition also contains reinforcing fibers in addition tothe thermoplastic polymer matrix.

Reinforcing fibers of which use may advantageously be made are mineralfibers, such as glass fibers, polymer fibers, in particular organichigh-modulus fibers, such as aramid fibers, or metal fibers, such assteel fibers, or carbon fibers or natural fibers, fibers from renewableresources.

These fibers may be in modified or unmodified form, e.g. provided with asizing, or chemically treated, in order to improve adhesion to theplastic. Glass fibers are particularly preferred.

Glass fibers are provided with a sizing to protect the glassfiber, tosmooth the fiber but also to improve the adhesion between the fiber andthe matrix material. A sizing usually comprises silanes, film formingagents, lubricants, wetting agents, adhesive agents optionallyantistatic agents and plasticizers, emulsifiers and optionally furtheradditives.

Specific examples of silanes are aminosilanes, e.g.3-trimethoxysilylpropylamine,N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane,N-(3-trimethoxysilanylpropyl)ethane-1,2-diamine,3-(2-aminoethyl-amino)propyltrimethoxysilane,N-[3-(trimethoxysilyl)propyl]-1,2-ethane-diamine.

Film forming agents are for example polyvinylacetates, polyesters andpolyurethanes. Sizings based on polyurethanes may be usedadvantageously.

The reinforcing fibers may be compounded into the polymer matrix, forexample in an extruder or kneader.

According to one embodiment, the molding composition of the presentdisclosure comprises at least one reinforcing fiber which is a mineralfiber, preferably a glass fiber, more preferably a coated or impregnatedglass fiber. Glass fibers which are suitable for the molding compositionof the present disclosure are commercially available, e.g. JohnsManville, ThermoFlow®Chopped Strand 753, OCV Chopped Strand 408 A,Nippon Electric Glass Co. (NEG) Chopped Strand T-651.

Fiber diameters can vary depending upon the particular fiber used andwhether the fiber is in either a chopped or a continuous form. Thefibers, for instance, can have a diameter of from about 5 μm to about100 μm, such as from about 5 μm to about 50 μm, such as from about 5 μmto about 15 μm. The length of the fibers can vary depending upon theparticular application. For instance, the fibers can have a length ofgreater than about 100 microns, such as greater than about 200 microns,such as greater than about 300 microns, such as greater than about 350microns. The length of the fibers can generally be less than about 1,000microns, such as less than about 800 microns, such as less than about600 microns, such as less than about 500 microns. Once incorporated intothe polymer composition and molded into an article, the fiber length candecrease. For instance, the average fiber length in the final productcan be from about 100 microns to about 400 microns, such as from about100 microns to about 300 microns.

In general, reinforcing fibers are present in the polymer composition inamounts sufficient to increase the tensile strength of the composition.The reinforcing fibers, for example, can be present in the polymercomposition in an amount greater than about 5% by weight, such as in anamount greater than about 10% by weight, such as in an amount greaterthan about 15% by weight, such as in an amount greater than about 20% byweight, such as in an amount greater than about 25% by weight, such asin an amount greater than about 30% by weight. The reinforcing fibersare generally present in an amount less than about 55% by weight, suchas in an amount less than about 50% by weight, such as in an amount lessthan about 45% by weight, such as in an amount less than about 40% byweight, such as in an amount less than about 35% by weight, such as inan amount less than about 30% by weight.

Tribological Modifier

According to the present disclosure, the polymer composition and thepolymer article comprising the reinforced polyester polymer compositionmay comprise at least one tribological modifier.

In one embodiment, ultra-high molecular weight silicone (UHMW-Si) may beused to modify the polyester polymer. In general, the UHMW-Si can havean average molecular weight of greater than 100,000 g/mol, such asgreater than about 200,000 g/mol, such as greater than about 300,000g/mol, such as greater than about 500,000 g/mol and less than about3,000,000 g/mol, such as less than about 2,000,000 g/mol, such as lessthan about 1,000,000 g/mol, such as less than about 500,000 g/mol, suchas less than about 300,000 g/mol. Generally, the UHMW-Si can have akinematic viscosity at 40° C. measured according to DIN 51562 of greaterthan 100,000 mm² s⁻¹, such as greater than about 200,000 mm² s⁻¹, suchas greater than about 1,000,000 mm² s⁻¹, such as greater than about5,000,000 mm² s⁻¹, such as greater than about 10,000,000 mm² s⁻¹, suchas greater than about 15,000,000 mm² s⁻¹ and less than about 50,000,000mm² s⁻¹, such as less than about 25,000,000 mm² s⁻¹, such as less thanabout 10,000,000 mm² s⁻¹, such as less than about 1,000,000 mm² s⁻¹,such as less than about 500,000 mm² s⁻¹, such as less than about 200,000mm² s⁻¹.

The UHMW-Silicone may comprise a siloxane such as a polysiloxane orpolyorganosiloxane. In one embodiment, the UHMW-Si may comprise adialkylpolysiloxane such as a dimethylsiloxane, an alkylarylsiloxanesuch as a phenylmethylsiloxane, a polysilsesquioxane, or adiarylsiloxane such as a diphenylsiloxane, or a homopolymer thereof suchas a polydimethylsiloxane or a polymethylphenylsiloxane, or a copolymerthereof with the above molecular weight and/or kinematic viscosityrequirements. The polysiloxane or polyorganosiloxane may also bemodified with a substituent such as an epoxy group, a hydroxyl group, acarboxyl group, an amino group or a substituted amino group, an ethergroup, or a meth(acryloyl) group in the end or main chain of themolecule. The UHMW-Si compounds may be used singly or in combination.Any of the above UHMW-Si compounds may be used with the above molecularweight and/or kinematic viscosity requirements.

The UHMW-Silicone may be added to the polymer composition as amasterbatch wherein the UHMW-Si is dispersed in a carrier polymer andthe masterbatch is thereafter added to the composition. The masterbatchmay comprise from about 10 wt. % to about 60 wt. %, such as from about35 wt. % to about 55 wt. %, such as about 50 wt. % of an UHMW-Si.

The carrier polymer can vary depending upon the particular applicationand the desired result. The carrier polymer for the ultra-high molecularweight silicone may comprise any thermoplastic polymer compatible withpolybutylene terephthalate. In one embodiment, for instance, the carrierpolymer may comprise a polyester polymer. Using a polyester polymer, forinstance, will assist in blending the ultra-high molecular weightsilicone polymer with the polybutylene terephthalate polymer. Thepolyester carrier polymer, for instance, may comprise polybutyleneterephthalate, polyethylene terephthalate, a copolyester, and/or apolyester elastomer. The polyester elastomer may comprise a copolyestersuch as a segmented thermoplastic copolyester. The polyester elastomer,for example, may comprise a multi-block copolymer. In an alternativeembodiment, the carrier polymer may comprise a polycarbonate polymer.

In an alternative embodiment, instead of using a carrier polymer, theultra-high molecular weight silicone polymer may be grafted ontoparticles that are then incorporated into the polymer composition. Forinstance, in one embodiment, the ultra-high molecular weight siliconepolymer can be grafted on metal oxide particles such as silicaparticles. The ultra-high molecular weight silicone grafted silica canthen be present in the composition in an amount greater than about 1% byweight, such as in an amount greater than about 2% by weight, such as inan amount greater than about 3% by weight, such as in an amount greaterthan about 4% by weight. The ultra-high molecular weight siliconegrafted silica is generally present in the composition in an amount lessthan about 20% by weight, such as in an amount less than about 15% byweight, such as in an amount less than about 10% by weight, such as inan amount less than about 6% by weight.

The UHMW-Silicone may be present in the polymer composition in an amountof at greater than about 0.005 wt. %, such as at greater than about 0.1wt. %, such as at greater than about 0.5 wt. %, such as at greater thanabout 0.75 wt. %, such as at greater than about 1 wt. %, such as atgreater than about 2 wt. %, such as at greater than about 2.5 wt. % andgenerally less than about 10 wt. %, such as less than about 6 wt. %,such as less than about 5 wt. %, such as less than about 4 wt. %, suchas less than about 3.5 wt. %, such as less than about 3 wt. %, whereinthe weight is based on the total weight of the polymer composition.

In an alternative embodiment, the at least one tribological additive maycomprise a fluoropolymer, such as polytetrafluoroethylene powder. Thefluoropolymer may be combined with the ultra-high molecular weightsilicone in one application. The polytetrafluoroethylene particles, forinstance, can have an average particle size of less than about 15microns, such as less than about 12 microns, such as less than about 10microns, such as less than about 8 microns. The average particle size ofthe polytetrafluoroethylene particles is generally greater than about0.5 microns, such as greater than about 1 micron, such as greater thanabout 2 microns, such as greater than about 3 microns, such as greaterthan about 4 microns, such as greater than about 5 microns. Averageparticle size can be measured according to ISO Test 13321.

In one embodiment, the polytetrafluoroethylene particles can have arelatively low molecular weight. The polytetrafluoroethylene polymer mayhave a density of from about 300 g/I to about 450 g/I, such as fromabout 325 g/I to about 375 g/I when tested according to ASTM Test D4895.The polytetrafluoroethylene particles can have a specific surface areaof from about 5 m²/g to about 15 m²/g, such as from about 8 m²/g toabout 12 m²/g when tested according to Test DIN66132. The melt flow rateof the polytetrafluoroethylene polymer can be less than about 3 g/10min, such as less than about 2 g/10 min when tested according to ISOTest 1133 when carried out at 372° C. with a load of 10 kg.

The polytetrafluoroethylene particles can be present in the polymercomposition in an amount greater than about 1% by weight, such as in anamount greater than about 2% by weight, such as in an amount greaterthan about 3% by weight, such as in an amount greater than about 4% byweight. The polytetrafluoroethylene polymer is generally present in thepolymer composition in an amount less than about 20% by weight, such asin an amount less than about 15% by weight, such as in an amount lessthan about 10% by weight, such as in an amount less than about 8% byweight.

According to the present disclosure, the tribological additives improvethe tribological properties of the polymer compositions and polymerarticles produced therefrom without the need for an external lubricant,such as water-based external lubricants, when utilized in tribologicalapplications. An external lubricant may be a lubricant that is appliedto a polymer article. In one embodiment, an external lubricant may notbe associated with the polymer composition or polymer article such thatthe external lubricant is not present on a surface of the polymercomposition or polymer article. In another embodiment, an externallubricant may be utilized with the polymer composition and polymerarticle of the present disclosure.

In addition to an ultra-high molecular weight silicone and/or apolytetrafluoroethylene polymer, the polymer composition may containother tribological modifiers. Other tribological modifiers that may bepresent include, for instance, boron nitride, ultra-high molecularweight polyethylene particles, stearyl stearate particles, waxes, andthe like. The other tribological modifiers can generally be present inan amount from about 0.5% to about 5% by weight, such as in an amountfrom about 1% to about 3% by weight.

Other Additives

The polymer composition of the present disclosure can contain variousother additives. For example, the composition may further include anucleating agent, present in a concentration of between about 0.1 and 2%by weight, preferably between about 0.001% and 0.5% based on the totalweight of the composition. The nucleating agent can be selected from thegroup consisting of alkali metal salts having anions which are oxides ofthe elements from Group IV of the Periodic Table; barium sulfate; andtalc.

The polymer composition may also contain at least one stabilizer. Thestabilizer may comprise an antioxidant, a light stabilizer such as anultraviolet light stabilizer, a thermal stabilizer, and the like.

Sterically hindered phenolic antioxidant(s) may be employed in thecomposition. Examples of such phenolic antioxidants include, forinstance, calcium bis(ethyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate) (Irganox® 1425);terephthalic acid,1,4-dithio-,S,S-bis(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) ester(Cyanox®1729); triethylene glycolbis(3-tert-butyl-4-hydroxy-5-methylhydrocinnamate); hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate (Irganox® 259);1,2-bis(3,5,di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazide(Irganox®1024); 4,4′-di-tert-octyldiphenamine (Naugalube®438R);phosphonic acid, (3,5-di-tert-butyl-4-hydroxybenzyl)-,dioctadecyl ester(Irganox® 1093); 1,3,5-trimethyl-2,4,6-tris(3′,5′-di-tert-butyl-4′hydroxybenzyl)benzene (Irganox®1330);2,4-bis(octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-trazine(Irganox® 565); isooctyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate(Irganox®1135); octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox®1076);3,7-bis(1,1,3,3-tetramethylbutyl)-10H-phenothiazine (Irganox® LO 3);2,2′-methylenebis(4-methyl-6-tert-butylphenol)monoacrylate (Irganox®3052);2-tert-butyl-6-[1-(3-tert-butyl-2-hydroxy-5-methylphenyl)ethyl]-4-methylphenylacrylate (Sumilizer® TM 4039);2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenylacrylate (Sumilizer® GS); 1,3-dihydro-2H-Benzimidazole (Sumilizer® MB);2-methyl-4,6-bis[(octylthio)methyl]phenol (Irganox®1520);N,N′-trimethylenebis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide(Irganox®1019); 4-n-octadecyloxy-2,6-diphenylphenol (Irganox® 1063);2,2′-ethylidenebis[4,6-di-tert-butylphenol](Irganox® 129); NN′-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide)(Irganox® 1098); diethyl (3,5-di-tert-butyl-4-hydroxybenxyl)phosphonate(Irganox®1222); 4,4′-di-tert-octyldiphenylamine (Irganox® 5057);N-phenyl-1-napthalenamine (Irganox® L 05);tris[2-tert-butyl-4-(3-ter-butyl-4-hydroxy-6-methylphenylthio)-5-methylphenyl]phosphite (Hostanox® OSP 1); zinc dinonyidithiocarbamate(Hostanox® VP-ZNCS 1);3,9-bis[1,1-diimethyl-2-[(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane(SumilizerS AG80); pentaerythrityltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate](Irganox®1010);ethylene-bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate(Irganox® 245); 3,5-di-tert-butyl-4-hydroxytoluene (Lowinox BHT,Chemtura) and so forth.

Some examples of suitable sterically hindered phenolic antioxidants foruse in the present composition are triazine antioxidants having thefollowing general formula:

wherein, each R is independently a phenolic group, which may be attachedto the triazine ring via a C₁ to C₅ alkyl or an ester substituent.Preferably, each R is one of the following formula (I)-(III):

Commercially available examples of such triazine-based antioxidants maybe obtained from American Cyanamid under the designation Cyanox® 1790(wherein each R group is represented by the Formula III) and from CibaSpecialty Chemicals under the designations Irganox® 3114 (wherein each Rgroup is represented by the Formula I) and Irganox® 3125 (wherein each Rgroup is represented by the Formula II).

Sterically hindered phenolic antioxidants may constitute from about 0.01wt. % to about 3 wt. %, in some embodiments from about 0.05 wt. % toabout 1 wt. %, and in some embodiments, from about 0.05 wt. % to about0.1 wt. % of the entire stabilized polymer composition. In oneembodiment, for instance, the antioxidant comprises pentaerythrityltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

Hindered amine light stabilizers (“HALS”) may be employed in thecomposition to inhibit degradation of the polyester composition and thusextend its durability. Suitable HALS compounds may be derived from asubstituted piperidine, such as alkyl-substituted piperidyl,piperidinyl, piperazinone, alkoxypiperidinyl compounds, and so forth.For example, the hindered amine may be derived from a2,2,6,6-tetraalkylpiperidinyl. Regardless of the compound from which itis derived, the hindered amine is typically an oligomeric or polymericcompound having a number average molecular weight of about 1,000 ormore, in some embodiments from about 1000 to about 20,000, in someembodiments from about 1500 to about 15,000, and in some embodiments,from about 2000 to about 5000. Such compounds typically contain at leastone 2,2,6,6-tetraalkylpiperidinyl group (e.g., 1 to 4) per polymerrepeating unit.

Without intending to be limited by theory, it is believed that highmolecular weight hindered amines are relatively thermostable and thusable to inhibit light degradation even after being subjected toextrusion conditions. One particularly suitable high molecular weighthindered amine has the following general structure:

wherein, p is 4 to 30, in some embodiments 4 to 20, and in someembodiments 4 to 10. This oligomeric compound is commercially availablefrom Clariant under the designation Hostavin® N30 and has a numberaverage molecular weight of 1200.

Another suitable high molecular weight hindered amine has the followingstructure:

wherein, n is from 1 to 4 and R₃₀ is independently hydrogen or CH3. Sucholigomeric compounds are commercially available from Adeka Palmarole SAS(joint venture between Adeka Corp. and Palmarole Group) under thedesignation ADK STAB® LA-63 (R₃₀ is CH3) and ADK STAB® LA-68 (R₃₀ ishydrogen).

Other examples of suitable high molecular weight hindered aminesinclude, for instance, an oligomer ofN-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-piperidinol and succinic acid(Tinuvin®622 from Ciba Specialty Chemicals, MW=4000): oligomer ofcyanuric acid and N,N-di(2,2,6,6-tetramethyl-4-piperdyl)-hexamethylenediamine;poly((6-morpholine-S-triazine-2,4-diyl)(2,2,6,6-tetramethyl-4-piperdinyl)-iminohexamethylene-(2,2,6,6-tetramethyl-4-piperidinyl)-imino)(Cyasorb® UV 3346 from Cytec, MW=1600);polymethylpropyl-3-oxy-[4(2,2,6,6-tetramethyl)-piperidinylysiloxane(Uvasil® 299 from Great Lakes Chemical, MW=1100 to 2500); copolymer ofα-methylstyrene-N-(2,2,6,6-tetramethyl-4-piperidinyl)maleimide andN-stearyl maleimide; 2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanoltetramethyl-polymer with 1,2,3,4-butanetetracarboxylic acid; and soforth. Still other suitable high molecular weight hindered amines aredescribed in U.S. Pat. No. 5,679,733 to Malik, et al. and U.S. Pat. No.6,414,155 to Sassi, et al., which are incorporated herein in theirentirety by reference thereto for all purposes.

In addition to the high molecular hindered amines, low molecular weighthindered amines may also be employed in the composition. Such hinderedamines are generally monomeric in nature and have a molecular weight ofabout 1000 or less, in some embodiments from about 155 to about 800, andin some embodiments, from about 300 to about 800.

Specific examples of such low molecular weight hindered amines mayinclude, for instance, bis-(2,2,6,6-tetramethyl-4-piperidyl) sebacate(Tinuvin® 770 from Ciba Specialty Chemicals, MW=481);bis-(1,2,2,6,6-pentamethyl-4-piperdinyl)-(3,5-ditert.butyl-4-hydroxybenzyl)butyl-propanedioate; bis-(1,2,2,6,6-pentamethyl-4-piperdinyl)sebacate;8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro-(4,5)-decane-2,4-dione,butanedioic acid-bis-(2,2,6,6-tetramethyl-4-piperidinyl) ester;tetrakis-(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate; 7-oxa-3,20-diazadispiro(5.1.11.2)heneicosan-20-propanoic acid, 2,2,4,4-tetramethyl-21-oxo, dodecyl ester;N-(2,2,6,6-tetramethyl-4-piperidinyl)-N′-amino-oxamide;o-t-amyl-o-(1,2,2,6,6-pentamethyl-4-piperidinyl)-monoperoxi-carbonate;β-alanine, N-(2,2,6,6-tetramethyl-4-piperdinyl), dodecylester;ethanediamide, N-(1-acetyl-2,2,6,6-tetramethylpiperdinyl)-N′-dodecyl;3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidinyl)-pyrrolidin-2,5-dione;3-dodecyl-1-(1,2,2,6,6-pentamethyl-4-piperidinyl)-pyrrolidin-2,5-dione;3-dodecyl-1-(1-acetyl,2,2,6,6-tetramethyl-4-piperidinyl)-pyrrolidin-2,5-dione,(Sanduvar® 3058 from Clariant, MW=448.7);4-benzoyloxy-2,2,6,6-tetramethylpiperidine;1-[2-(3,5-di-tert-butyl-4-hydroxyphenylpropionyloxy)ethyl]-4-(3,5-di-tert-butyl-4-hydroxylphenylpropionyloxy)-2,2,6,6-tetramethyl-piperdine;2-methyl-2-(2″,2″,6″,6″-tetramethyl-4″-piperidinylamino)-N-(2′,2′,6′,6′-tetra-methyl-4′-piperdinyl)propionylamide;1,2-bis-(3,3,5,5-tetramethyl-2-oxo-piperazinyl)ethane;4-oleoyloxy-2,2,6,6-tetramethylpiperidine; and combinations thereof.Other suitable low molecular weight hindered amines are described inU.S. Pat. No. 5,679,733 to Malik, et al.

The hindered amines may be employed singularly or in combination in anyamount to achieve the desired properties, but typically constitute fromabout 0.01 wt. % to about 4 wt. % of the polymer composition.

UV absorbers, such as benzotriazoles or benzopheones, may be employed inthe composition to absorb ultraviolet light energy. Suitablebenzotriazoles may include, for instance,2-(2-hydroxyphenyl)benzotriazoles, such as2-(2-hydroxy-5-methylphenyl)benzotriazole:2-(2-hydroxy-5-tert-octylphenyl)benzotriazole (Cyasorb® UV 5411 fromCytec); 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzo-triazole;2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole;2-(2-hydroxy-3,5-dicumylphenyl)benzotriazole;2,2′-methylenebis(4-tert-octyl-6-benzo-triazolylphenol); polyethyleneglycol ester of 2-(2-hydroxy-3-tert-butyl-5-carboxyphenyl)benzotriazole;2-[2-hydroxy-3-(2-acryloyloxyethyl)-5-methylphenyl]-benzotriazole;2-[2-hydroxy-3-(2-methacryloyloxyethyl)-5-tert-butylphenyl]benzotriazole;2-[2-hydroxy-3-(2-methacryloyloxyethyl)-5-tert-octylphenyl]benzotriazole;2-[2-hydroxy-3-(2-methacryloyloxyethyl)-5-tert-butylphenyl]-5-chlorobenzotriazole;2-[2-hydroxy-5-(2-methacryloyloxyethyl)phenyl]benzotriazole;2-[2-hydroxy-3-tert-butyl-5-(2-methacryloyloxyethyl)phenyl]benzotriazole;2-[2-hydroxy-3-tert-amyl-5-(2-methacryloyloxyethyl)phenyl]benzotriazole;2-[2-hydroxy-3-tert-butyl-5-(3-methacryloyloxypropyl)phenyl]-5-chlorobenzotriazole;2-[2-hydroxy-4-(2-methacryloyloxymethyl)phenyl]benzotriazole;2-[2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropyl)phenyl]benzotriazole;2-[2-hydroxy-4-(3-methacryloyloxypropyl)phenyl]benzotriazole; andcombinations thereof.

Exemplary benzophenone light stabilizers may likewise include2-hydroxy-4-dodecyloxybenzophenone: 2,4-dihydroxybenzophenone;2-(4-benzoyl-3-hydroxyphenoxy)ethyl acrylate (Cyasorb® UV 209 fromCytec); 2-hydroxy-4-n-octyloxy)benzophenone (Cyasorb® 531 from Cytec);2,2′-dihydroxy-4-(octyloxy)benzophenone (Cyasorb® UV 314 from Cytec);hexadecyl-3,5-bis-tert-butyl-4-hydroxybenzoate (Cyasorb® UV 2908 fromCytec); 2,2′-thiobis(4-tert-octylphenolato)-n-butylamine nickel(II)(Cyasorb® UV 1084 from Cytec); 3,5-di-tert-butyl-4-hydroxybenzoic acid,(2,4-di-tert-butylphenyl)ester (Cyasorb® 712 from Cytec);4,4′-dimethoxy-2,2′-dihydroxybenzophenone (Cyasorb® UV 12 from Cytec);and combinations thereof.

When employed, UV absorbers may constitute from about 0.01 wt. % toabout 4 wt. % of the entire polymer composition.

In one embodiment, the polymer composition may contain a blend ofstabilizers that produce ultraviolet resistance and color stability. Thecombination of stabilizers may allow for products to be produced thathave bright and fluorescent colors. In addition, bright colored productscan be produced without experiencing significant color fading over time.In one embodiment, for instance, the polymer composition may contain acombination of a benzotriazole light stabilizer and a hindered aminelight stabilizer, such as an oligomeric hindered amine.

If desired, fatty acid esters may be present as lubricants. Fatty acidesters may be obtained by oxidative bleaching of a crude natural wax andsubsequent esterification of the fatty acids with an alcohol. Thealcohol typically has 1 to 4 hydroxyl groups and 2 to 20 carbon atoms.When the alcohol is multifunctional (e.g., 2 to 4 hydroxyl groups), acarbon atom number of 2 to 8 is particularly desired. Particularlysuitable multifunctional alcohols may include dihydric alcohol (e.g.,ethylene glycol, propylene glycol, butylene glycol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol and 1,4-cyclohexanediol), trihydricalcohol (e.g., glycerol and trimethylolpropane), tetrahydric alcohols(e.g., pentaerythritol and erythritol), and so forth. Aromatic alcoholsmay also be suitable, such as o-, m- and p-tolylcarbinol, chlorobenzylalcohol, bromobenzyl alcohol, 2,4-dimethylbenzyl alcohol,3,5-dimethylbenzyl alcohol, 2,3,5-cumobenzyl alcohol,3,4,5-trimethylbenzyl alcohol, p-cuminyl alcohol, 1,2-phthalyl alcohol,1,3-bis(hydroxymethyl)benzene, 1,4-bis(hydroxymethyl)benzene,pseudocumenyl glycol, mesitylene glycol and mesitylene glycerol.Particularly suitable fatty acid esters for use in the present inventionare derived from montanic waxes. Licowax® OP (Clariant), for instance,contains montanic acids partially esterified with butylene glycol andmontanic acids partially saponified with calcium hydroxide. Thus,Licowax® OP contains a mixture of montanic acid esters and calciummontanate. Other montanic acid esters that may be employed includeLicowax® E, Licowax® OP, and Licolub® WE 4 (all from Clariant), forinstance, are montanic esters obtained as secondary products from theoxidative refining of raw montan wax. Licowax® E and Licolub®WE 4contain montanic acids esterified with ethylene glycol or glycerine.

Other known waxes may also be employed in a lubricant. Amide waxes, forinstance, may be employed that are formed by reaction of a fatty acidwith a monoamine or diamine (e.g., ethylenediamine) having 2 to 18,especially 2 to 8, carbon atoms. For example, ethylenebisamide wax,which is formed by the amidization reaction of ethylene diamine and afatty acid, may be employed. The fatty acid may be in the range from C₁₂to C₃₀, such as from stearic acid (Cia fatty acid) to formethylenebisstearamide wax. Ethylenebisstearamide wax is commerciallyavailable from Lonza, Inc. under the designation Acrawax® C, which has adiscrete melt temperature of 142° C. Other ethylenebisamides include thebisamides formed from lauric acid, palmitic acid, oleic acid, linoleicacid, linolenic acid, oleostearic acid, myristic acid and undecalinicacid. Still other suitable amide waxes areN-(2-hydroxyethyl)12-hydroxystearamide and N,N′-(ethylenebis)12-hydroxystearamide.

In addition to the above components, the polymer composition may includevarious other ingredients. Colorants that may be used include anydesired inorganic pigments, such as titanium dioxide, ultramarine blue,cobalt blue, and other organic pigments and dyes, such asphthalocyanines, anthraquinones, and the like. Other colorants includecarbon black or various other polymer-soluble dyes. The colorants cangenerally be present in the composition in an amount up to about 2percent by weight.

Polymer Articles

The compositions of the present disclosure can be compounded and formedinto a polymer article using any technique known in the art. Forinstance, the respective composition can be intensively mixed to form asubstantially homogeneous blend. The blend can be melt kneaded at anelevated temperature, such as a temperature that is higher than themelting point of the polymer utilized in the polymer composition butlower than the degradation temperature. Alternatively, the respectivecomposition can be melted and mixed together in a conventional single ortwin screw extruder. Preferably, the melt mixing is carried out at atemperature ranging from 150 to 300° C., such as from 200 to 280° C.,such as from 220 to 270° C. or 240 to 260° C. However, such processingshould be conducted for each respective composition at a desiredtemperature to minimize any polymer degradation.

After extrusion, the compositions may be formed into pellets. Thepellets can be molded into polymer articles by techniques known in theart such as injection molding, thermoforming, blow molding, rotationalmolding and the like. According to the present disclosure, the polymerarticles demonstrate excellent tribological behavior and mechanicalproperties. Consequently, the polymer articles can be used for severalapplications where low wear and excellent gliding properties aredesired.

Polymer articles include any moving articles or moldings that are incontact with another surface and may require high tribologicalrequirements. For instance, polymer articles include articles for theautomotive industry, especially housings, latches such as rotarylatches, window winding systems, wiper systems, pulleys, sun roofsystems, seat adjustments, levers, bushes, gears, gear boxes, claws,pivot housings, wiper arms, brackets or seat rail bearings, zippers,switches, cams, rollers or rolling guides, sliding elements or glidessuch as sliding plates, conveyor belt parts such as chain elements andlinks, castors, fasteners, levers, conveyor system wear strips and guardrails, medical equipment such as medical inhalers and injectors. Analmost limitless variety of polymer articles may be formed from thepolymer compositions of the present disclosure.

In one embodiment, the composition of the present disclosure is used toproduce a first sliding member and a second sliding member. The firstand second sliding members can both be made from a composition inaccordance with the present disclosure. In particular, the first slidingmember and the second sliding member can be made from a compositioncomprising a reinforced polyester polymer in combination with anultrahigh molecular weight silicone and optionally a fluoropolymer. Therelative amounts of the components can be the same or can be differentin each composition.

The first sliding member and the second sliding member can be containedin an apparatus and placed in operative association with each other suchthat the sliding members move relative to each other. For instance, inone embodiment, the first sliding member may be stationary while thesecond sliding member moves across the first sliding member.Alternatively, both sliding members may move while contacting eachother.

In one embodiment, the sliding members of the present disclosure can beused to produce a medical product. For instance, referring to FIG. 1, aninhaler 20 is shown. The inhaler 20 includes a housing 22 attached to amouthpiece 24. In operative association with the housing 22 is a plunger26 for receiving a canister containing a composition to be inhaled. Thecomposition may comprise a spray or a powder. The inhaler 20 can includea first sliding member in operative association with a second slidingmember. For instance, in certain embodiments, the housing 22 maycomprise the first sliding member while the plunger 26 may comprise thesecond sliding member. Alternatively, the first sliding member maycomprise the housing 22 and the second sliding member may comprise themouthpiece 24. In still another embodiment, an internal sliding membermay be contained within the housing 22 that slides relative to thehousing.

During use, the inhaler 20 administers metered doses of a medication,such as an asthma medication to a patient. The asthma medication may besuspended or dissolved in a propellant or may be contained in a powder.When a patient actuates the inhaler to breathe in the medication, avalve opens allowing the medication to exit the mouthpiece.

In another embodiment of the present disclosure, the first slidingmember and the second sliding member are contained in a medical injector30 as shown in FIG. 2. The medical injector 30 includes a housing 32 inoperative association with a plunger 34. The housing 32 or first slidingmember may slide relative to the plunger 34 or second sliding member.The medical injector 30 may be spring loaded. The medical injector 30 isfor injecting a drug into a patient, typically into the thigh or thebuttocks. The medical injector can be needleless or may contain aneedle. When containing a needle, the needle tip is typically shieldedwithin the housing prior to injection. Needleless injectors, on theother hand, can contain a cylinder of pressurized gas that propels amedication through the skin without the use of a needle.

Properties

The polyester polymer composition and polymer articles producedtherefrom according to the present disclosure have improved tribologicalproperties. According to the present disclosure, the tribologicalproperties are generally measured by the coefficient of friction.

In general, static friction is the friction between two or more surfacesthat are not moving relative to each other (i.e., both objects arestationary). In general, dynamic friction occurs when two objects aremoving relative to each other (i.e., at least one object is in motion orrepeated back and forth motion). In addition, stick-slip is generallyknown as a phenomenon caused by continuous alternating between staticand dynamic friction.

According to the present disclosure, the composition and polymer articlemay exhibit a dynamic coefficient of friction against another surface,as determined according to VDA 230-206, of less than about 0.08, such asless than about 0.07, such as less than about 0.06, such as less thanabout 0.05.

In one embodiment, the above dynamic coefficient of friction values andeffect of sliding speed on the dynamic coefficient of friction areexhibited between the composition or polymer article and variouscounter-materials. For instance, the above values may be exhibitedbetween the composition or polymer article and an identical compositionor article.

The counter-material may also comprise a polycarbonate polymercomposition containing 20% by weight glass fiber and 15% by weightpolytetrafluoroethylene particles. In another embodiment, thecounter-material comprises a polybutylene terephthalate compositioncontaining 20% by weight glass fiber and 15% by weightpolytetrafluoroethylene particles.

While the polymer composition and polymer articles produced therefrom ofthe present disclosure provide improved tribological properties, thecompositions and articles may also exhibit improved mechanicalproperties. For instance, the tensile modulus, determined according toISO Test No. 527, of the composition or polymer article may be greaterthan about 7000 MPa, such as greater than about 7200 MPa, such asgreater than about 7500 MPa, and generally less than about 15,000 MPa,such as less than about 10,000 MPa.

The break stress of the composition can generally be greater than about100 MPa, such as greater than about 110 MPa, such as greater than about115 MPa, such as greater than about 120 MPa and generally less thanabout 180 MPa. The break strain can generally be greater than about2.0%, such as greater than about 2.5%, and generally less than about 4%.The composition can exhibit a Charpy notched impact strength when testedat 23° C. of greater than about 6 kJ/m², such as greater than about 8kJ/m², such as greater than about 9 kJ/m² and generally less than about20 kJ/m², such as less than about 15 kJ/m².

The present disclosure may be better understood with reference to thefollowing examples.

EXAMPLE

The following example is given below by way of illustration and not byway of limitation. The following experiments were conducted in order toshow some of the benefits and advantages of the present invention.

Various polymer compositions containing glass fibers and a tribologicalmodifier were formulated and tested for friction characteristics andphysical properties. Each of the compositions contained a polybutyleneterephthalate polymer and glass fibers in an amount of 22% by weight. Anultra-high molecular weight silicone was then added to the compositionwith different carriers. In one embodiment, for instance, the carrierwas silica particles. In other embodiments, however, the carrier was apolycarbonate polymer or a thermoplastic polyester elastomer. Some ofthe compositions also contained 5% by weight polytetrafluoroethyleneparticles. One formulation only contained polytetrafluoroethyleneparticles as the tribological modifier.

The components of each respective composition were mixed together andcompounded using a ZSK 25MC (Werner & Pfleiderer, Germany) twin screwextruder. The screw configuration with kneading elements was chosen sothat effective thorough mixing of the components took place. Thecompositions were extruded and pelletized. The pellets were dried for 8hours at 120° C. and then injection molded.

The compositions/molds were tested for a variety of tribological andphysical properties.

In this example, the tribological properties were determined for variouscompositions.

Stick-slip tests were conducted to determine the dynamic coefficient offriction. Stick-slip tests were conducted according to VDA 230-206. Aball-on-plate configuration was utilized with a load of 30 N, a slidingspeed of 8 mm/s, and a test duration of 1000 cycles.

The compositions formulated according to the present disclosure wereformed into plates for the dynamic coefficient of friction test. In afirst set of experiments, the compositions were tested against a ballmade from polycarbonate polymer containing 20% by weight glass fiber and15% by weight polytetrafluoroethylene particles. The following resultswere obtained:

TABLE 1 Triboadditives in Dynamic Wear track No. PBT with 22% GF CoFwidth (mm) 1 5% PTFE 0.094 0.44 2 5% PTFE + 4.3% UHMW-Si 0.07 0.45grafted Silica 3 5% PTFE + 3% UHMW-Si 0.043 0.66 (50% blend in PC) 4 5%PTFE + 3% UHMW-Si 0.044 0.53 (50% blend in thermoplastic polyesterelastomer) 5 3% UHMW-Si (50% blend in 0.039 0.57 thermoplastic polyesterelastomer)

In a second set of experiments, the ball was made from a polymercomposition containing polybutylene terephthalate polymer combined with20% by weight glass fiber and 15% by weight polytetrafluoroethyleneparticles. The following results were obtained:

TABLE 2 Triboadditives in Dynamic Wear track No. PBT with 22% GF CoFwidth (mm) 1 5% PTFE 0.093 0.33 2 5% PTFE + 4.3% UHMW-Si 0.068 0.12grafted Silica 3 5% PTFE + 3% UHMW-Si 0.043 0.2 (50% blend in PC) 4 5%PTFE + 3% UHMW-Si 0.041 0.15 (50% blend in thermoplastic polyesterelastomer) 5 3% UHMW-Si (50% blend in 0.044 0.19 thermoplastic polyesterelastomer)

In a third set of experiments, the ball was made from the identicalpolymer composition. The following results were obtained:

TABLE 3 Triboadditives in Dynamic Wear track No. PBT with 22% GF CoFwidth (mm) 1 5% PTFE 0.091 0.34 2 5% PTFE + 4.3% UHMW-Si 0.07 0.18grafted Silica 3 5% PTFE + 3% UHMW-Si 0.042 0.23 (50% blend in PC) 4 5%PTFE + 3% UHMW-Si 0.043 0.19 (50% blend in thermoplastic polyesterelastomer) 5 3% UHMW-Si (50% blend in 0.045 0.24 thermoplastic polyesterelastomer)

The compositions were also tested for physical properties. Tensileproperties were tested according to ISO Test 527:2012. Notched Charpyimpact strength was tested according to ISO Test 179-1:2010. The testwas run using a Type A notch (0.25 mm base radius) and Type 1 specimensize (length of 80 mm, width of 10 mm, and thickness of 4 mm). The testwas conducted at a temperature of 23° C. The following results wereobtained:

TABLE 4 Triboadditives in PBT with 22% GF 5% PTFE + 3% UHMW-Si 3%UHMW-Si 5% PTFE + 5% PTFE + (50% blend in (50% blend in 4.3% UHMW-Si 3%UHMW-Si thermoplastic thermoplastic Property 5% PTFE grafted Silica (50%blend in PC) polyester elastomer) polyester elastomer) Tensile modulus(MPa) 8280 7705 7810 7780 7750 Break stress (MPa) 136 115 122 120 121Break strain (%) 2.9 2.8 2.9 2.7 2.6 Charpy notched @ 23° C. 9.3 9.8 1010.5 10.1 (kJ/m²)

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

What is claimed:
 1. A polymer composition that can be compounded orextruded into a polymer article comprising: a polyester polymer, thepolyester polymer comprising a polybutylene terephthalate polymer aloneor in combination with a polyethylene terephthalate polymer, thepolybutylene terephthalate polymer being present in the polymercomposition in an amount greater than 40% by weight; reinforcing fiberspresent in the polymer composition in an amount from about 5% to about55% by weight; and a masterbatch comprising a first tribologicalmodifier dispersed in a carrier polymer, the first tribological modifiercomprising an ultra-high molecular weight silicone having a kinematicviscosity of greater than 100,000 mm² s⁻¹, the ultra-high molecularweight silicone being present in the polymer composition in an amountfrom about 0.5% by weight to about 6% by weight, the ultra-highmolecular weight silicone being present in the masterbatch in an amountfrom about 35% by weight to about 60% by weight.
 2. A polymercomposition that can be compounded or extruded into a polymer article asdefined in claim 1, wherein the ultra-high molecular weight silicone isa polydimethylsiloxane.
 3. A polymer composition that can be compoundedor extruded into a polymer article as defined in claim 1, wherein thecomposition contains a second tribological modifier.
 4. A polymercomposition that can be compounded or extruded into a polymer article asdefined in claim 3, wherein the polybutylene terephthalate polymer ispresent in the composition in an amount from about 50% to about 90% byweight, the reinforcing fibers comprising glass fibers and being presentin the polymer composition in an amount from about 5% to about 30% byweight, and the ultra-high molecular weight silicone dispersed withinthe carrier polymer being present in the composition in an amount fromabout 0.5% to about 5% by weight.
 5. A polymer composition that can becompounded or extruded into a polymer article as defined in claim 1,wherein the composition is isocyanate free.
 6. A polymer compositionthat can be compounded or extruded into a polymer article as defined inclaim 1, wherein the polymer composition exhibits a dynamic coefficientof friction according to VDA 230-206 of less than 0.08 when testedagainst polycarbonate containing 15% by weight polytetrafluoroethyleneand 20% by weight glass fiber, when tested against polybutyleneterephthalate containing 15% by weight polytetrafluoroethylene and 20%by weight glass fiber, or when tested against itself at a speed of 8mm/s, at a load of 30 N and after 1,000 cycles.
 7. A polymer compositionthat can be compounded or extruded into a polymer article as defined inclaim 1, wherein the polymer composition exhibits a dynamic coefficientof friction according to VDA 230-206 of less than 0.07 when testedagainst polycarbonate containing 15% by weight polytetrafluoroethyleneand 20% by weight glass fiber, when tested against polybutyleneterephthalate containing 15% by weight polytetrafluoroethylene and 20%by weight glass fiber, or when tested against itself at a speed of 8mm/s, at a load of 30 N and after 1,000 cycles.
 8. A polymer compositionthat can be compounded or extruded into a polymer article as defined inclaim 1, wherein the polymer composition exhibits a dynamic coefficientof friction according to VDA 230-206 of less than 0.05 when testedagainst polycarbonate containing 15% by weight polytetrafluoroethyleneand 20% by weight glass fiber, when tested against polybutyleneterephthalate containing 15% by weight polytetrafluoroethylene and 20%by weight glass fiber, or when tested against itself at a speed of 8mm/s, at a load of 30 N and after 1,000 cycles.
 9. A polymer compositionthat can be compounded or extruded into a polymer article as defined inclaim 1, wherein the reinforcing fibers comprise glass fibers, the glassfibers being present in the polymer composition in an amount from about10% to about 30% by weight.
 10. A polymer composition that can becompounded or extruded into a polymer article as defined in claim 1,wherein the composition exhibits a Charpy notched impact strength ofgreater than 9 kJ/m² at 23° C.
 11. An apparatus comprising: a firstsliding member in operative association with a second sliding member,the first sliding member and the second sliding member being configuredto remain in contact and move relative to each other, at least one ofthe sliding members comprising a molded polymeric article made from apolymer composition comprising a polyester polymer, the polyesterpolymer comprising a polybutylene terephthalate polymer alone or incombination with a polyethylene terephthalate polymer or a polycarbonatepolymer, the polybutylene terephthalate polymer being present in thepolymer composition in an amount greater than 40% by weight; reinforcingfibers present in the polymer composition in an amount from about 5% toabout 55% by weight; a masterbatch comprising a first tribologicalmodifier dispersed in a carrier polymer, the first tribological modifiercomprising an ultra-high molecular weight silicone having a kinematicviscosity of greater than 100,000 mm² s⁻¹; and wherein the first slidingmember and the second sliding member are both made from the same polymercomposition.
 12. An apparatus as defined in claim 11, wherein theapparatus is a medical inhaler or injector.
 13. A polymer compositionthat can be compounded or extruded into a polymer article comprising: apolyester polymer, the polyester polymer comprising a polybutyleneterephthalate; a masterbatch comprising a tribological modifiercomprising an ultra-high molecular weight silicone having a kinematicviscosity of greater than 100,000 mm² s⁻¹ dispersed in a carrierpolymer, the ultra-high molecular weight silicone being present in anamount of from about 0.1% to about 6% by weight based upon the weight ofthe polymer composition, the ultra-high molecular weight silicone beingpresent in an amount of from about 10% to about 60% by weight based uponthe weight of the combination of the ultra-high molecular weightsilicone and the carrier polymer; and a second tribological modifiercomprising a fluoropolymer powder having an average particle size ofless than 15 microns and greater than 0.5 microns, the fluoropolymerpowder having a melt flow rate of less than 3 g/10 min.
 14. A polymercomposition that can be compounded or extruded into a polymer article asdefined in claim 13, wherein the second tribological modifier comprisesa polytetrafluorethylene.
 15. A polymer composition that can becompounded or extruded into a polymer article as defined in claim 13,wherein the ultra-high molecular weight silicone is apolydimethylsiloxane.